int exchangeBits(int num){
    unsigned int addnum, evenum;
    addnum = num & 0x55555555;   //与0B01010101...0101得到奇数位
    evenum = num & 0xaaaaaaaa;   //与0B10101010...1010 偶数位
    //交换奇偶位
    addnum <<= 1;
    evenum >>= 1;

    return addnum + evenum;

}